The present invention pertains to a self-centering element for clamping workpieces between clamping jaws, which are associated with self-centering slides and are moved by means of deflecting pins arranged in pairs.
Self-centering elements have the task of clamping workpieces in a centered manner. It is important in this connection that the clamping jaws that receive and hold the workpiece be guided accurately and move toward each other without a clearance. It is known that the clamping jaws can be moved by means of a toothed rack and a pinion, the consequence of which is that the retaining force is only as high as the clamping force itself Thus, all the forces acting on the workpiece during the machining adversely affect the holding action. The prior-art spindle drives with right-left threads have the drawback that they are not free from clearance. It Is important for the workpiece to be held securely and for its position not to be compromised by a machining force.
A device for a clamping unit has been known (EP 0 386 295 B1), in which deflecting pins are inserted in pairs for transmitting the driving forces, and these deflecting pins transmit the force in opposite directions via wedge surfaces and wedge bevels. Such a self-centering element is provided with a driving slide, which is guided longitudinally in the housing and is associated with a pair of deflecting pins each moving in opposite directions. The deflecting pins act in turn on self-centering slides via wedge bevels. This has the advantage that the frictional forces are very high and retaining forces that amount to a multiple of the clamping force are generated as a consequence of the double deflection of the movement by means of wedge bevels. However, the deflecting pins stand upright above the mounting surface of the element and thus determine the overall height, which in turn determines how far away from the machine table the clamped workpiece is mounted. Thus, the leverage of the clamping jaws above the machine table is added to the longitudinal and transverse forces, which may lead to twisting.
Thus, the object of the present invention is to design a clamping element such that it can make do with a smaller overall height by the force being introduced into the deflecting pins horizontally in a plane directly below the plane of the self-centering slides and by the wedge mechanism being arranged horizontally, i.e., in parallel to the mounting surface.
The advantage of such an arrangement is that workpieces can be moved as close to the mounting surface of the clamping element on the machine table as possible and the vibrations that are otherwise generated during the machining of the workpieces are thus very extensively eliminated. Moreover, this arrangement in one plane causes, due to the position of the deflecting pins and of the movements of all parts involved, which movements are associated therewith, that a very high retaining force will build up, so that the position and holding of workpieces once clamped cannot be affected by the machining forces any longer.
According to the invention, a self-centering unit for clamping workpieces between clamping jaws is provided. The clamping jaws are associated with centering slides, with deflecting pins, which are arranged in pairs in a housing between a linkage and the self-centering slides and which bring about the transmission of forces from the linkage to the self- centering slides via wedge surfaces. Four recesses are provided in which two such deflecting pins, each cooperating in pairs, are slidingly guided. The four recesses are milled in the housing in a plane located in parallel to the mounting surface of the unit. The deflecting pins are provided with wedge bevels at the head end and slide on the wedge surfaces, which are associated with two pistons. The pistons are guided in the same plane in a cylindrical hole or region provided at right angles to the recesses. Displacement of the pairs of deflecting pins in opposite directions is brought about by the movement of the pistons. The self-centering slides are slidingly guided via carrier prisms in the deflecting pins and can be displaced at right angles to the direction of movement of the deflecting pins and are guided in a second plane located in parallel directly above the deflecting pins.
The deflecting pins may be provided over a partial area with a groove. Such a groove may have a straight limiting surface toward the end of the deflecting pin, and the groove may be limited by an oblique surface opposite this limiting surface.
One of the carrier prisms provided with two bevels can be inserted into each pair of deflecting pins such that the bevels are in contact with the oblique surfaces of the deflecting pins and are guided slidingly. The carrier prism may be connected to the self-centering slide.
The pistons may be actuated hydraulically via hydraulic connections. The movement of the pistons displaces the deflecting pins in pairs and in opposite directions via the wedge surfaces and the wedge bevel. The carrier prisms located in the grooves may be moved by the deflecting pins toward the outside away from one another or toward the inside toward one another as a consequence of the displacement of the deflecting pins in opposite directions, so that the self-centering slides connected to the carrier prisms bring about the clamping operation.
The position of the self-centering slides and consequently the position of the deflecting pins and pistons can be monitored and scanned by sensors.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which a preferred embodiment of the invention is illustrated.